Description:
Since version 6.3.6, a presentation containing basic animation effects (appear on click) is displayed correctly only in forward direction (objects show up sequentially in response to a mouse click or a cursor down-right, page-down key press). When presentation is scrolled back (cursor up-left, page-up key), however, objects do not disappear one by one in reverse order as expected, but rather in an unpredictable sequence and often in pairs. When the presentation direction is reversed again (forward), some objects do not reappear, unless reversal has occurred at the beginning of a slide. LO versions <= 6.3.2 are seemingly not affect by this bug, although thin white strips superimposed to objects occasionally appear on scrolling back.


Steps to Reproduce:
1. Create a one-slide new presentation, create/insert a few objects (any type: text boxes, images, etc.) and enable "appear on click" animation effect on them.
2. Start presentation, click mouse or press right, down cursor key to make objects show up.
3. When the last object has appeared, press left, up cursor or page-up key to rewind presentation.

Actual Results:
At point 3 (presentation rewind) objects disappear in erratic sequence and often  in pairs.

Expected Results:
At point 3 (presentation rewind) objects should disappear one by one in reverse order of their creation. 


Reproducible: Always


User Profile Reset: Yes


OpenGL enabled: Yes

Additional Info:
BUG PRESENT in

Version: 6.3.6.2
Build ID: 3.6.2-4.fc31
CPU threads: 4; OS: Linux 5.3; UI render: default; VCL: gtk3; 
Locale: en-US (en_US.UTF-8); UI-Language: en-US
Calc: threaded

Version: 7.0.4.2
Build ID: dcf040e67528d9187c66b2379df5ea4407429775
CPU threads: 4; OS: Linux 5.0; UI render: default; VCL: gtk3
Locale: en-US (en_US.UTF-8); UI: en-US
Calc: threaded

BUG PRESENT also in LO >= 6.4 on Windows 10 (64 bit)


Bug is NOT PRESENT in 

Version: 6.3.2.2
Build ID: 6.3.2.2-1.fc31
CPU threads: 4; OS: Linux 5.3; UI render: default; VCL: gtk3; 
Locale: en-US (en_US.UTF-8); UI-Language: en-US
Calc: threaded